The present invention relates generally to data acquisition devices and sample rate reduction equipment and methods therefor.
Modern scientific analysis of complex events frequently requires the acquisition of voluminous data. Various sophisticated systems are used to gather data about a device for phenomenon being investigated and to refine the data so that it is comprehensible to an engineer or scientist. Generally, a large number of parameters must be monitored, and frequently the density of information is extremely high. For example, to test a reactor core cooling system, the dynamic stress on each of the reactor rods must be monitored, as well as all other paremeters which vary during reactor operation. Accordingly, a system may be required to receive and process two hundred or more data channels. The overall system would include means for acquiring the raw data at each channel and means for processing the data.
The acquisition, processing and recording of the entire continuum of data occurring over many channels is frequently impossible due to the extremely high information volume and/or density. To alleviate this problem, samples of data in each channel are taken, and it is only the samples which are recorded and processed. However, a substantial quantity of data still remains. So, because in a data gathering and/or evaluation system there generally exists a maximum frequency of interest which is known beforehand, the art has sought to further alleviate the problem by ignoring samples for data above that maximum frequency of interest. In accordance with the Nyquist sampling theory, to sample adequately any continuum of data, at least two samples are required for each cycle at the maximum frequency of the data. Ideally then, a system which gathers data for subsequent processing, i.e. a data acquisition system, could sample the continuous data at twice that known maximum frequency of interest to reduce to an absolute minimum the data which are needed to describe the input continuum adequately.
However, in practice, great expense is required to approach the ideal lower limit. The signal conditioner unit for each data channel typically includes a pre-sample filter (sometimes called an anti-aliasing filter), but since two hundred or more channels may be required, filter matching and expense becomes a problem. Therefore, data acquisition systems in current use compromise expense with performance and typically include three- to five-pole filters. It has been found necessary, though, when using such filters, to increase the sampling rate typically to five times the maximum frequency of interest in order to obtain samples to describe the data without excess alias error. This in turn regenerates problems where high density data acquisition is required: the greater the number of samples, the greater the burden on the processing and recording equipment. Taking samples at five times the maximum frequency of interest yields 2.5 times as much data as are theoretically necessary to describe the phenomenon.
It is therefore the primary object of the present invention to provide a data acquisition system which provides fewer samples than are typically taken to describe adequately a phenomenon under investigation without sacrificing sample accuracy and at a reasonable cost.